Re: Zass question

On Thu, 4 Aug 2005 23:10:47 -0700, Johnny wrote:
>

> I recently bought a zass 169dg and yes it does exactly as you describe. It
> was so bad I looked into why and was unimpressed with the machining of the
> rotor burr in 2 ways. Firstly the the thread was not tapped axially in the
> burr and secondly the burr plane is offset from the plane of the burr body.
> Seems to me this would cause the end to wobble although I don't see why one
> edge wouldn't always contact tyhe stator burr.
> My old zass 151 did the same a little but the new 169 is way worse. Looks
> like about a 0.020 inch run-out. Sigh.
> I've put some photos on the web at
> http://members.cox.net/fullcity/zassburr/ some of which compare a 12 yr
> old zass 151 rotor burr with the new 169 burr.
>: Johnny

The short version: If it was assembled first
and then machined, (much of) the runout could be an
optical illusion.

The longer version:
Most likely the internal threads were drilled and
tapped before the burr was milled and the shaft used
in a collet while the burr was machined.
Since the hole was either not centered, or not
parallel to the axis of the burr body, then the
machined cutting edges on the burr (even though
concentric with the shaft) would appear to be much
farther out than they actually are.
This would be quite common, and even almost
expected when starting out with a casting.

If you really wanted to see what's what, you
could put the shaft in a V-block (or pair of them),
and rotate it with a reference (pointer, plane, or
dial indicator) on/near the the cutting edges of the
burr.

- Steve "precision grinding for nuclear submarine
reactor parts, and aircraft landing gear were us"
Ackman
.

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